The invention is generally directed to toner compositions, and more specifically, the present invention is directed to developer and toner compositions containing therein charge enhancing additives, which impact a negative charge to the toner resin particles. In one embodiment there is provided in accordance with the present invention toner compositions comprised of resin particles, pigment particles, and iron complex charge enhancing additives, including the iron complex of azo dyes prepared from coupling dye diazotized substituted amino phenols with substituted naphthols. The aforementioned toner compositions can be selected for the development of electrostatic latent images inclusive of color images. Additionally, these additives are believed to be nontoxic in that, for example, they would generate an acceptable negative Ames test. Developer compositions with charge enhancing additives, which impart a positive charge to the toner resin are well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. There is also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica.
Also, there is disclosed in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonates. Further, there is disclosed in U.S. Pat. No. 4,298,672 positively charged toner compositions with resin particles and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds. Additionally, other patents disclosing positively charged toner compositions with charged control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 and 4,394,430.
Moreover, toner compositions with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The U.S. Pat. No. 4,411,974 patent discloses negatively charged toner compositions comprised of resin particles, pigment particles, and as a charge enhancing additive ortho-halo phenyl carboxylic acids. Similarly, there is disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives.
There is illustrated in U.S. Pat. No. 4,404,271, the disclosure of which is totally incorporated herein by reference, a complex system for developing electrostatic images with a toner which contains a metal complex represented by the formula in column 2, lines 20 to 31; and wherein ME can be chromium, cobalt or iron. Additionally, other patents disclosing various metal containing azo dyestuff structures wherein the metal is chromium or cobalt include U.S. Pat. Nos. 2,891,939; 2,871,233; 2,891,938; 2,933,489; 4,053,462 and 4,314,937. Also, in U.S. Pat. No. 4,433,040, the disclosure of which is totally incorporated herein by reference, there are illustrated toner compositions with chromium and cobalt complexes of azo dyes as negative charge enhancing additives.
Although many charge control additives are known, there continues to be a need for new additives. Specifically, there continues to be a need for additives which will impart negative charges and stable triboelectric characteristics to toner resin particles. Moreover, there continues to be a need for humidity insensitive negatively charged toner and developer compositions. Further, there is a need for charge enhancing additives which can be easily and permanently dispersed into toner resin particles. There also is a need for negatively charged toner compositions with desirable and rapid toner admix charging characteristics.